Surface treatment process for fabricating a panel of an organic light emitting device

ABSTRACT

A surface treatment process for fabricating a panel of an organic light emitting device is disclosed. The surface treatment process for fabricating a panel of an organic light emitting device comprises following steps: forming on a substrate a plurality of first electrodes; forming a plurality of ramparts having T-shape cross-section on said substrate and selectively on said first electrodes through coating positive chemically amplified photoresist compositions having photo-acid generators on said substrate, exposing coated substrate to UV radiation to form latent pattern, post-exposure surface treating said photoresist on said substrate in a alkaline atmosphere and developing said photoresist; wherein each rampart protruding from said substrate and having an overhanging portion projecting in a direction parallel to said substrate; depositing organic electroluminescent media to the exposed area between said ramparts on said substrate; forming a plurality of second electrodes on said organic electroluminescent media on said substrate.

FIELD OF THE INVENTION

[0001] The present invention relates to a surface treatment process forfabricating a panel of an organic light emitting device (OLED),especially associates to a surface treatment process for the isolatingwalls on a panel of an OLED.

BACKGROUND OF THE INVENTION

[0002] The latest OLED dominated a focus of developing flat paneldisplay (FPD) technology in recent years. Compared with other FPDs suchas LCDs (liquid crystal displays) and FEDs (Field emission displays),OLED display panels have many distinguished advantages such as lightweight, high contrast, fast response speed, low power consumption andhigh brightness. However, there are many technical problems in the massproduction and commercialization of OLED urgently needed to be solved.

[0003] For example, in the fabrication of OLED, the alignment ofelectrodes and prevention of short circuits between electrodes is stillvery important to the patterning and pixel quality of OLED. So far, theshadow mask process is widely applied in the fabrication of OLED toresolve such alignment problems of electrodes on the display panel ofOLED. However, because multiple layers of different organic materialsand cathode materials have to be deposited, it is difficult to useexternal shadow masks to accurately align each layer to form patterns onthe substrate of panels, especially for the alignment of patterns withhigh resolution of multiple layers.

[0004] On the other hand, OLED with good display quality such aslifetime and reliability, simple processing method, low price, higherresolution, and thinner display panel (i.e. less thickness) isimmediately necessary now. Nevertheless, because there are manytechnical problems still require to be overcome, the resolution and thethickness of OLED still cannot be effectively improved at the same time.Recently, several technologies are proposed to improve the processing ofOLED, but obvious improvement on resolution and thickness of OLEDs isstill very rare.

[0005] For example, Burrowa et al. disclosed a technology to form amultiple intrinsic shadow mask layer having an undercut on the substrateof display panel to accurately align the organic functional mediums andelectrodes (e.g. anodes) in U.S. Pat. No. 6,013,538. The intrinsicshadow mask layer proposed by Burrowa et al. is made by multiplematerials and complicated process. The cost of materials is high forthis multiple shadow mask because many different materials are needed.The yield of this multiple shadow mask process is limited becausecomplicate processing steps are required, too. In U.S. Pat. No.5,962,970 Yokoi et al. disclosed another method to fabricate panels oforganic light emitting devices. Yokoi et al. revealed in U.S. Pat. No.5,962,970 a method to form a pattern of isolating layer havingreverse-trapezoid cross-section to work as an intrinsic shadow mask anda wall to separate cathode materials from anodes for improving thedisplay quality of the panels. However, the thickness (height) and theresolution of the isolating layer having reverse-trapezoid cross-sectionare limited. The thickness (or height) of isolating layer is required tobe high enough (e.g. at least more than 6 μm) to avoid possible shortcircuits resulted from direct contact of cathode materials and anodes.As cathode formed through deposition, cathode materials will deposit onthe protruding part of isolating layer. To avoid direct contact betweenanode and cathode materials deposited on the side walls of insulatinglayers (owing to lateral diffusion of cathode materials in evaporativedirections), the isolating layer having reverse-trapezoid cross-sectionshould be wide enough to act as shadow walls to separate anode materialsfrom cathode to avoid possible shorts. If the height of isolating layeris too low, the protruding part of the isolating layer will be not wideenough to separate the side-deposited cathode materials from contactinganodes. Thus, the thickness and the width of the isolating layer havingreverse-trapezoid cross section cannot be effectively reduced. Thereforethe corresponding resolution and the thickness of the panel of the OLEDis limited. On the other hand, since the shape of the isolating layer isreverse-trapezoid, the width of the base of the isolating layer isnarrower than the width of top. The width of the base of the isolatinglayer having reverse-trapezoid cross section are required to be wideenough to support the isolating layer and exempt from collapsing ofisolating layer. The average minimum width of the isolating layerprocessed by the method taught in U.S. Pat. No. 5,962,970 is around 15μm. The average minimum height of the isolating layer processed by themethod described in U.S. Pat. No. 5,962,970 is around 6 μm. Thecorresponding resolution and the thickness of the panel of the OLED issignificantly limited.

[0006] In 1997, another method for manufacturing organic emittingdevices is disclosed in U.S. Pat. No. 5,701,055. Nagayama et al.disclosed a technology to form isolating layers on panel substrate toavoid direct contact between cathode materials and anodes in U.S. Pat.No. 5,701,055. In U.S. Pat. No. 5,701,055, isolating layers havingmulti-layer T-shaped cross-section or reverse-trapezoid cross-section isformed on the substrate to avoid direct contact between cathodematerials and anodes. Thus the isolation between anodes and cathodes oforganic light emitting devices can be solved. Nevertheless, theisolating layers having T-shaped cross-section mutilayer disclosed inU.S. Pat. No. 5,701,055 are made by more than two materials. Multiplemasks and lithographic processes are required for the formation ofisolating layers having T-shaped cross-section in U.S. Pat. No.5,701,055. The method for forming isolating layers having T-shapedcross-section in U.S. Pat. No. 5,701,055 solved the isolation betweenanodes and cathodes of OLED. However, the complicate steps of the methodfor forming isolating layers having T-shaped cross-section in U.S. Pat.No. 5,701,055 cost expensive because many different materials, reagentsand complex processes are required. So far, the OLEDs meeting all therequirements such as relatively simple fabricating process, low cost,less material consumption, capability of mass production, highreproducible yield, high resolution and relatively low thickness are notdisclosed yet and still in urgently demand now.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is to provide a surfacetreatment process for fabricating a panel of an OLED having relativelyhigh resolution and relatively low thickness.

[0008] Another object of the present invention is to provide a surfacetreatment process for preventing possible shorts of a panel of an OLED.

[0009] Another object of the present invention is to provide a surfacetreatment process of a panel of an OLED for facilitating the process,reducing cost and increasing the yield

[0010] Another object of the present invention is to provide a surfacetreatment process for preventing OLEDs from shorts caused by lateraldiffusion and collapse of the surface layers of OLEDs.

[0011] The surface treatment process for fabricating a panel of an OLEDof the present invention comprising following steps: forming on asubstrate a plurality of first electrodes; forming a plurality oframparts having T-shape cross-section on said substrate and selectivelyon said first electrodes through coating positive chemically amplifiedphotoresist compositions having photo-acid generators on said substrate,exposing coated substrate to ultraviolet (UV) radiation to form latentpatterns, post-exposure surface-treating said photoresist on saidsubstrate in an alkaline atmosphere and developing said photoresist;wherein each rampart protruding from said substrate and having anoverhanging portion projecting in a direction parallel to saidsubstrate; depositing organic electroluminescent media to the exposedareas between said ramparts on said substrate; forming a plurality ofsecond electrodes on said organic electroluminescent media on saidsubstrate.

[0012] The OLEDs of the present invention comprise: a substrate on whicha plurality of first electrodes are formed; a plurality of rampartshaving T-shape cross-section formed on said substrate and selectively onsaid first electrodes through coating positive chemically amplifiedphotoresist compositions having photo-acid generators on said substrate,exposing coated substrate to UV radiation to form latent patterns,post-exposure surface-treating said photoresist on said substrate in analkaline atmosphere and developing said photoresist; wherein eachramparts protruding from said substrate and having an overhangingportion projecting in a direction to said substrate; an organic functionlayers which includes at least one organic electroluminescent mediumformed on the exposed areas between ramparts; and a plurality of secondelectrodes formed on organic functional layer.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 is a partially enlarged perspective view of the panel ofthe present invention before formation of organic electroluminescentmedium and second electrodes.

[0014]FIG. 2 is the cross-section view showing the panel achieved by thesurface treatment process of the present invention.

[0015]FIG. 3 is a picture of top view of partial OLED panel made by theprocess illuminated in example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The surface treatment process of the present invention forfabricating a panel of an OLED having a plurality of emitting portionsincludes forming a plurality of first electrodes on a substrate atfirst. Then a plurality of ramparts having T-shape cross-section isformed on the substrate and selectively on the first electrodes. Suchramparts formed on the substrate and first electrodes are made throughcoating positive chemically amplified photoresist compositions havingphoto-acid generators on the substrate, exposing coated substrate to UVradiation to form latent patterns, post-exposure surface-treating saidphotoresist on said substrate in an alkaline atmosphere and developingsaid photoresist. The ramparts on the substrate protrudes from thesubstrate and having an overhanging portion projecting in a directionparallel to the substrate. Subsequently, organic electroluminescentmedia is formed to the exposed area between ramparts on the substrate.Furthermore, a plurality of second electrodes is formed on the organicelectroluminescent media on the substrate to form a panel of an OLED.

[0017] The formation of first electrodes can be formed in patterns onsubstrate through conventional photolithography. There is no limit forthe patterns of first electrodes. However, patterns of stripes inparallel of first electrodes are preferred. The materials of firstelectrodes can be any conductive materials. Preferably, the firstelectrodes are transparent conductive materials such as InTiO₃, InSnO₃(ITO), SnO₂, CdSnO, In₂O₃ doped with ZnO or antimony. The surfacetreatment process of the present invention can also selectively containsstep of forming a plurality of auxiliary electrodes on the substratethrough photolithography before forming first electrodes on thesubstrate. The formation of auxiliary electrodes is to increase theconductivity of first electrodes. The auxiliary electrodes are formed byprocessing substrates which are deposited by conductive materials beforephotolithography. The materials of auxiliary electrodes can be anyconductive materials. Preferably, the auxiliary electrodes are made bychromium, aluminium, copper or silver. The patterns of auxiliaryelectrodes made through photolithography can be any form of patterns.Preferably, the auxiliary electrodes are parallel to first electrodesformed subsequently.

[0018] A pixel-defining layer can be selectively formed after firstelectrodes are formed. The pixel-defining layer can be formed inpatterns through photolithography. The pixel-defining layer functions asan additional protective layer to isolate anodes and cathodes. Thepatterns of pixel-defining layer are not limited. However, patterns ofpixel-defining layer with open portions above first electrodes arepreferred. The pixel-defining layer can be any electrically insulatedmaterials. Preferably, the pixel-defining layer is polyimide.

[0019] The ramparts on the panel of the OLEDs are made of positivechemically amplified photoresist compositions that contain photo-acidgenerators. The positive chemically amplified photoresist compositionsalso contain at least a polymer in addition to photo-acid generators.Preferably, the polymers used in the chemically amplified photoresistcompositions are polymers having pendant tert-butoxyl carbonyl (t-BOC)protective groups connected to the backbone of the polymers. Mostpreferably, polymers of the positive chemically amplified photoresistcompositions are polymers with following structures:

[0020] The positive chemically amplified photoresist compositions canfurther selectively contain other additives such as acid quenchers orsolvents to improve the characteristics of the photoresist compositionsor the ramparts. Any UV radiation that can initiate the photo-reactionof photoacid generators of the positive chemically amplified photoresistcompositions can be adequate radiation sources for the process of thepresent invention. Preferably, the wavelength of adequate radiationsource is about 254 nm. The poaitive chemically amplified photoresistcompositions are used to form a plurality of ramparts having T-shapecross-section on the substrate. The ramparts having T-shapecross-section are formed by utilizing the interaction of the photo-acidgenerators and the UV radiation. The mechanism of forming rampartshaving T-shape cross-section is accepted as following: As positivechemically amplified photoresist compositions exposed to radiation withadequate wavelength (e.g. wavelength about 254 nm), the photo-acidgenerators are initiated to release photo-acid anions. The releasedphoto-acid anions are activated by following post-exposuresurface-treating step. The activated photo-acid anions then react (e.g.deprotection) with the polymers in the positive chemically amplifiedphotoresist compositions. The reaction is also catalyzed by photo-acidanions themselves to accelerate the reaction rates. As post-exposuresurface treatment by alkaline atmosphere, the reaction catalyzed andinitiated by photo-acid anions will be neutralized or quenched in thepart near close to the surface of the area exposed to UV radiation. Theregion of quench or neutralization is only located on the surface ofphotoresist. Therefore, after post-exposure surface-treated in thealkaline atmosphere, the unexposed area of the positive chemicallyamplified photoresist compositions will form latent protruding rampartshaving T-shape cross-section on substrates. The ramparts formed on thesubstrate by post-exposure surface-treating the positive chemicallyamplified photoresist compositions in alkaline atmosphere and developingthe radiation-exposed positive chemically amplified photoresistcompositions. The ramparts having T-shape cross-section is a seriousdrawback to be improved in the IC fabrication of semiconductor, though.Now, the ramparts having T-shape cross-section formed on the substrateof panels of OLEDs act as ideal shadow masks for subsequent depositionprocesses and serves as isolating walls to separate side-depositedcathode materials from anodes. The overhanging parts of the T-shapecross-section can provide enough area and length for subsequentdeposition of cathode materials and further prevent direct contact ofcathode materials and anodes. The side-deposition of cathode materialsis owing to the lateral diffusion of cathode materials as cathodematerials evaporated. Hence, the reduction of photoresist thickness inthis invention is significantly beneficial to decrease the possibilityof lateral diffusion during cathode evaporation and meet the reliableyield and thin tendency of OLED panels. The alkaline atmosphere can beany atmosphere of alkaline solution. Preferably, the alkaline atmosphereis the atmosphere or vapors of tetramethyl amonium hydroxide (TMAH) orpotassium hydroxide that come from tetramethyl amonium hydroxide orpotassium hydroxide solution. The patterns of the ramparts can bepatterns having open portions above first electrodes. Patterns inparallel strides and intersecting the first electrodes are preferable.

[0021] Organic electroluminescent media are formed after a plurality offirst electrodes and ramparts are formed. The organic electroluminescentmedia are deposited on the substrate and selectively on firstelectrodes. The organic electroluminescent media are deposited as asingle layer or optionally multiple layers (e.g. HTL, EL, ETL) on thesubstrate and selectively on first electrodes.

[0022] A plurality of second electrodes is then formed on the organicelectroluminescent media on the substrate. The formation of secondelectrodes can be formed through conventional deposition methods. Theorganic electroluminescent media is sandwiched by second electrodes andfirst electrodes on the substrate. The open portions where firstelectrodes and second electrodes between ramparts are the emittingportions (i.e. pixels) of OLED. The second electrodes can be anyelectrically conductive materials. Preferably, the second electrodes areMgAg, aluminium, diamond, diamondlike or calcium.

[0023] The substrate that applied in the process of the presentinvention can be transparent or not transparent. Preferably, thesubstrates used in the present invention are sodalime glasses, boronsilica glasses, plastics or silicon wafers.

[0024] The ramparts formed through the surface treatment process of thepresent invention have relative stable bases (column base) than otherramparts formed through known other methods. The angles between thesubstrate and the column base of ramparts of the present invention areclose to 90°. The nearly vertical base of ramparts support the rampartssolidly and prevent ramparts from collapsing. Compared with rampartshaving reverse-trapezoid cross-section, the ramparts having T-shapecross-section are relatively strong and not apt to collapse. Even thewidth of the base of the ramparts is less than 1 μm (e.g. 0.18 μm), theramparts having T-shape cross-section stand very well withoutcollapsing. The height of the ramparts of the present invention doesn'tneed to be high. Even the height of the ramparts having T-shapecross-section is less than 6 μm (e.g. 4 μm), the ramparts having T-shapecross-section stand very well without collapsing. Therefore, theresolution of the OLEDs can be upgraded and the thickness the OLEDs canbe reduced at the same time through the surface treatment process of thepresent invention. Besides, the ramparts of the present invention canreduce the deposition of second electrodes caused by lateral diffusion.The relative long overhanging part of the ramparts having T-shapecross-section provides enough wide or long area for isolating theside-deposition of second electrode material. Therefore, the possibilityof short circuits resulted from direct contact of the first electrodesand the second electrode materials can be effectively reduced. On theother hand, the ramparts of the present invention are made by singlematerial with single photolithography, the cost and complexity ofphotolithographic process decrease significantly.

[0025]FIG. 1 is a partially enlarged perspective view of the panel ofthe present invention before formation of organic electroluminescentmedium and second electrodes. A plurality of auxiliary electrodes 70 isformed on the substrate 10 in parallel strides. Then a plurality offirst electrodes 20 is formed in parallel stripes on the substrate 10.The first electrodes 20 are almost in the same height and each firstelectrode cover two auxiliary electrodes 70. A pixel-defining layer 60in a pattern of multiple pixel windows is formed on the substrate 10 andfirst electrodes 20 subsequently. The open windows of the pixel-defininglayer 60 locate above part of the first electrodes 20. Each stride offirst electrodes 20 is separated into several open areas by thepixel-defining layer 60. A plurality of ramparts 50 which protrudes onthe substrate 10 and have T-shape cross-section is formed on thepixel-defining layer 60 and the substrate 10. The ramparts 50 have anoverhanging portion projecting in a direction parallel to the substrate10. The ramparts 50 are in a pattern of parallel strides and cross overthe first electrodes 20 perpendicularly. The open portions betweenramparts 50 are above the open window areas of pixel-defining layer 60.The open window areas of pixel-defining layer 60 are the locations offuture pixels after subsequent organic electroluminescent media 30 andsecond electrodes 40 form.

[0026]FIG. 2 is the cross-section view showing the panel achieved by thesurface treatment process of the present invention. The auxiliaryelectrodes 70, first electrodes 20, pixel-defining layer 60 are formedas illustrated above. The organic electroluminescent media 30 is formedthrough deposition on the first electrodes 20 between ramparts 50. Thesecond electrodes 40 are formed on the organic electroluminescent media30 subsequently.

[0027] The organic light emitting device formed by the surface treatmentprocess comprises a substrate on which a plurality of first electrodesare formed; a plurality of ramparts in T-top shape cross-section formedon said substrate and selectively on said first electrodes throughcoating positive chemically amplified phototesist compositions havingphoto-acid generators on said substrate, exposing coated substrate to UVradiation to form pattern, post-exposure surface-treating saidphotoresist on said substrate in a alkaline atmosphere and developingsaid photoresist; wherein each ramparts protruding from said substrateand having an overhanging portion projecting in a direction to saidsubstrate; an organic function layers which includes at least oneorganic electroluminescent medium formed on the exposed areas betweenramparts; and a plurality of second electrodes formed on organicfunctional layer.

[0028] The OLEDs achieved through the surface treatment process of thepresent invention can be applied to any display of images, graphs,symbols, letters and characters for any apparatus. Preferably, the OLEDsof the present invention are applied to the display of televisions,computers, printers, screens, vehicles, signal machines, communicationdevices, telephones, lights, electric books, microdisplays, fishingmachines, personal digital assistants (PDA), game machines, game gogglesand airplanes.

[0029] More detailed examples are used to illustrate the presentinvention, and these examples are used to explain the present invention.The examples below, which are given simply by way of illustration, mustnot be taken to limit the scope of the invention.

EXAMPLE 1

[0030] A panel of an OLED was fabricated through the surface treatmentprocess of the present invention.

[0031] ITO anodes were formed in a pattern of stripes on a cleaned glasssubstrate. Then a positive chemically amplified photoresist (APEX resistfrom Shipley corp.) composition was spin-coated on the substrate. Thecoated substrate was prebaked in ovens. A mask with a pattern in stridesis applied as the coated photoresist was exposed to radiation (deep UV).The exposed substrate was post-exposure baked and surfacely treated withTMAH atmosphere at the same time. Ramparts of photoresist are formed ina parallel-stride pattern. The strides of ramparts formed are alsoperpendicular to the strides of ITO. The ramparts formed on thesubstrate have T-shape cross-section. The width of ramparts strides isabout 0.18 μm and the height of ramparts is about 0.8 μm. Then theexposed portions between ramparts are deposited by TPD(N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) at a700 Å thickness. Subsequently, Alq₃ is deposited on the same area at a500 Å thickness. MaAg was deposited on the same area at a 1000 Åthickness to form a panel of an OLED.

EXAMPLE 2

[0032] A glass substrate which was coated with a layer of chromium andITO was used as the substrate. The auxiliary electrodes were formedthrough photolithography in a pattern of parallel strides. Then ITOelectrodes are formed in a pattern of parallel strides as described inexample 1. Then a polyimide was coated on the substrate and form apattern through photolithography and curing at a temperature of 300° C.Then the ramparts were formed as described in example 1. The substratewith polyimide pixel-defining layer, first electrodes and auxiliaryelectrodes was shown in FIGS. 1 and 2. Subsequent deposition of organicelectroluminescent layer and MgAg was achieved as described inexample 1. Then a panel of an OLED was achieved through the surfacetreatment process of the present invention.

[0033] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and, withoutdeparting from the scope thereof, can make various changes andmodifications of the invention to adapt it to various usages andconditions. Thus, other embodiments are also within the claims.

What is claimed is:
 1. A surface treatment process for fabricating apanel of an OLED having a plurality of emitting portions, comprising thesteps of: a. forming on a substrate a plurality of first electrodes; b.forming a plurality of ramparts having T-shape cross-section on saidsubstrate and selectively on said first electrodes through coatingpositive chemically amplified photoresist compositions having photo-acidgenerators on said substrate, exposing coated substrate to UV radiationto form latent pattern, post-exposure surface-treating said photoresiston said substrate in an alkaline atmosphere and developing saidphotoresist; wherein each rampart protruding from said substrate andhaving an overhanging portion projecting in a direction parallel to saidsubstrate; c. depositing organic electroluminescent media to the exposedarea between said ramparts on said substrate; d. forming a plurality ofsecond electrodes on said organic electroluminescent media on saidsubstrate.
 2. The process of claim 1 further comprising forming apixel-defining layer on said substrate and selectively on said firstelectrodes before forming a plurality of ramparts; wherein saidpixel-defining layer is made by polyimide.
 3. The process of claim 1,wherein said positive chemically amplified photoresist compositionscomprising polymers having pedant t-butoxy carbonyl (t-BOC) protectivegroups.
 4. The process of claim 1, wherein said first electrodes areperpendicularly intersected with said ramparts.
 5. The process of claim1, wherein said first electrodes are transparent.
 6. The process ofclaim 1, wherein said substrate is transparent.
 7. The process of claim1, wherein said substrate is post-exposure surface-treated in analkaline atmosphere and developed by an alkaline solution.
 8. Theprocess of claim 1, wherein said substrate is post-exposuresurface-treated in an atmosphere of tetramethyl amonium hydroxide. 9.The process of claim 1, wherein said substrate is post-exposuresurface-treated in an atmosphere of potassium hydroxide.
 10. The processof claim 1, wherein the thickness of said ramparts of chemical amplifiedphotoresist is less than 6 μm.
 11. The process of claim 1, furthercomprising forming a plurality of auxiliary electrodes on substratebefore forming a plurality of first electrodes on said substrate.
 12. Anorganic light emitting device having a plurality of emitting portionscomprising: a substrate on which a plurality of first electrodes areformed; a plurality of ramparts having T-shape cross-section formed onsaid substrate and selectively on said first electrodes through coatingpositive chemically amplified photoresist compositions having photo-acidgenerators on said substrate, exposing coated substrate to UV radiationto form latent pattern, post-exposure surface-treating said photoresiston said substrate in a alkaline atmosphere and developing saidphotoresist; wherein each ramparts protruding from said substrate andhaving an overhanging portion projecting in a direction to saidsubstrate; an organic function layers which includes at least oneorganic electroluminescent medium formed on the exposed areas betweenramparts; and a plurality of second electrodes formed on organicfunctional layers.
 14. The device of claim 13 further comprising aplurality of auxiliary electrodes on said substrate.
 15. The device ofclaim 13, wherein said ramparts are perpendicularly cross said firstelectrodes.
 16. The device of claim 13 further comprising apixel-defining polyimide layer selectively on substrate and firstelectrodes.
 17. The device of claim 13, wherein the thickness of saidramparts is less than 6 μm.